1. Technical Field
The disclosure relates to an inverter.
2. Related Art
Conventionally, an inverter that drives motors of various kinds of devices has been required to reduce size and weight in order to reduce cost and to be installed in an electrical room having a limited space. When an inverter is used outdoor or in a factory environment having dust and the like, high sealing performance is required for obtaining high dust proofing and water proofing property such as IP66 as environment-resistant performance.
In an inverter, a power semiconductor element that controls current flowing into a motor generates heat due to conduction loss upon application of current and switching loss occurring in transition of on/off. For these reasons, an air-cooled cooler and a water-cooled cooler are attached to an inverter in order to reduce heat generated by a power semiconductor element. However, in an inverter with, for example, an air-cooled cooler, a structural member of the air-cooled cooler occupies a large volume. There may be a case where a structural member of an air-cooled cooler occupies a volume ten times as large as or more than that of a power semiconductor module depending on setting conditions.
To reduce the size of an inverter, reduction in the size of a cooler is required. The size of a cooler can be reduced by reducing loss of a power semiconductor element and making a power semiconductor element usable at a higher temperature. Loss of a power semiconductor element can be reduced by advance of the power semiconductor element. Making a power semiconductor element usable at a higher temperature largely depends on advance of a package technique such as highly reliable bond including solder. Today, a maximum junction temperature of a power semiconductor element is 175 degrees Celsius, and there are power semiconductor elements having an allowable junction temperature in continuous driving up to 175 degrees Celsius.